The present invention relates generally to data storage devices, and more particularly, but not by limitation, to an apparatus and associated method that facilitate collision detection during write operations.
Disc drives of the type known as xe2x80x9cWinchesterxe2x80x9d disc drives or hard disc drives are well known in the industry. Such disc drives record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a spindle motor.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent to the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator housing is mounted to the pivot shaft, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an arcuate path.
As the physical size of disc drives has decreased historically, the physical size of many of the disc drive components has also decreased to accommodate this size reduction. Similarly, the density of the data recorded on the magnetic media has been greatly increased. In order to accomplish this increase in data density, significant improvements in both the recording heads and recording media have been made.
For instance, the first rigid disc drives used in personal computers had a data capacity of only 10 megabytes, and were in the format commonly referred to in the industry as the xe2x80x9cfull height, 5xc2xcxe2x80x3 format. Disc drives of the current generation typically have a data capacity of many gigabytes in a 3xc2xdxe2x80x3 package which is only one fourth the size or less of the full height, 5xc2xcxe2x80x3 format. Even smaller standard physical disc drive package formats, such as 2xc2xdxe2x80x3 and 1.8xe2x80x3, have been established. In order for these smaller envelope standards to gain market acceptance, even greater recording densities must be achieved.
The recording heads used in disc drives have evolved from monolithic inductive heads to composite inductive heads (without and with metal-in-gap technology) to thin-film heads fabricated using semi-conductor deposition techniques to the current generation of thin-film heads incorporating inductive write and magneto-resistive (MR) read elements. This technology path was necessitated by the need to continuously reduce the size of the gap in the head used to record and recover data, since such a gap size reduction was needed to reduce the size of the individual bit domain and allow greater recording density.
Since the reduction in gap size also meant that the head had to be closer to the recording medium, the quest for increased data density also lead to a parallel evolution in the technology of the recording medium. The earliest Winchester disc drives included discs coated with xe2x80x9cparticulatexe2x80x9d recording layers. That is, small particles of ferrous oxide were suspended in a non-magnetic adhesive and applied to the disc substrate. With such discs, the size of the magnetic domain required to record a flux transition was clearly limited by the average size of the oxide particles and how closely these oxide particles were spaced within the adhesive matrix. The smoothness and flatness of the disc surface was also similarly limited. However, since the size of contemporary head gaps allowed data recording and retrieval with a head flying height of about twelve microinches (0.000012 inches) or greater, the surface characteristics of the discs were adequate for the times.
Disc drives of the current generation incorporate heads that fly at nominal heights of a few microinches or less. Obviously, with nominal flying heights in this range, the surface characteristics of the disc medium must be much more closely controlled than was the case only a short time ago.
To ensure that data is correctly written to a track of the magnetic media in the disc drive, the recording head should be kept within the center of the recording track and its flight height kept within desired tolerances. While off-track errors can be detected by the servo positioning system, flight height errors are less easily detectable. Flight height errors are introduced when vertical vibrations are introduced on the arm where the recording head is mounted. One of the possible causes of such vibration is the collision of the recording head with foreign objects on the disc media. Another possible cause of such vibration is when the entire drive itself is subjected to a severe physical shock. During read operations this problem is currently addressed as the thermal asperity (TA) symptom. This symptom is characterized by a sudden change in resistance in the MR element that is used to read data from the disc media. However, during the write operation, such head collisions with foreign objects on the media generally remain undetected. As a result, data is written to the media with the recording head oscillating in a vertical manner resulting in a recorded signal of inconsistent amplitude being recorded into the media. This recorded signal may not be able to read back subsequently.
While attempts have been made to identify collisions that occur during write operations, such attempts generally involve relatively complex algorithms that necessitate addition computational overhead. For example, U.S. Pat. No. 6,097,559 to Ottesen et al. describes a system and method for detecting head-to-disc contact in-situ for a direct access storage device using a position error signal. The ""559 patent describes obtaining position error signal measurement values for several revolutions and storing such values in memory. The patent further describes using a processor to calculate the non-repeatable run-out (NRRO) values associated with the position error signals. The NRRO power ratios are disclosed as an indication of intermittent disc contact.
While previous attempts have provided some indication of head-collisions during write operations, they have involved added complexity and the associated performance decrease for processor overhead, reducing their suitability for full-time use during all write operations. Thus, there exists a need to provide simple detection of head collisions during write operations without increasing complexity or adding substantial component costs.
An apparatus and associated method for detecting head collision with disc media, or other matter, in a disc drive during a write operation is disclosed. A method in accordance with one embodiment includes monitoring the resistance of an MR element on the head in order to detect a temperature increase indicative of a head collision. The resistance can be compared to a pre-selected threshold to generate an output indicative of head collision.